The present invention is directed toward an improved construction member, and more specifically, toward a construction member such as a joist adapted to withstand stresses applied in several different directions as occur when the joist is used in a modular home being transported on a trailer.
Joists and other construction members made of natural dimensional wood are becoming increasingly expensive and hard to obtain because the old growth wood of large diameter and high strength used for such members is itself becoming rare and expensive. Second growth lumber is not an acceptable substitute because of its limited size and strength. However it is desirable that second growth lumber be used whenever possible to minimize the use of larger, solid natural wood members.
The use of engineered construction members such as joists has increased in recent years to take advantage of the lower cost of second growth lumber. Such joists generally comprise upper and lower chords formed from second growth lumber or laminated veneer lumber connected by one of several means. One such joist uses a solid and continuous plywood or oriented strand board (OSB) web member running the length of the chords. Since OSB can be produced from wood that is unsuitable for many other structural uses, the lower cost of the materials used offsets much of the additional cost associated with manufacturing the member. Another type of engineered joist uses dimensional lumber chords joined by a combination of metal webs and vertical lumber webs attached to the top and bottom chords with metal plates. Still another uses wood struts attached between the upper and lower chords, some normal to the chords and others angled with respect thereto. These member may be finger jointed and glued to the top and bottom chords, for example.
Another advantage of engineered products over dimensional lumber is that these products can readily be made to any size and configuration required by industry, and can be made in a consistent manner so that they are uniformly straight and lightweight. It is also easier to control the strength and other properties of engineered lumber than natural lumber, and this allows manufacturers to provide products of consistent quality that are in high demand. The many through-openings between the upper and lower chords also makes the installation of wiring and plumbing in a structure much easier when engineered joists are used because the drilling required when dimensional lumber is used is reduced or eliminated. Engineered members are less expensive to install than dimensional lumber and can even be designed to provide specific load-bearing characteristics when necessary. And, when the ends of such construction members are provided with trimmable web sections between the upper and lower chords, these member can easily be trimmed at a work site to the exact dimensions needed, just like natural wood products.
While such engineered joist perform admirably, there are still problems that remain to be addressed. For example, when webs are added to the ends of such members to make them trimmable, it is generally necessary to glue the web to the upper and lower chords of the construction member and clamp the member while it dries. If the member is not clamped, the upper and lower chords may spread or the distance therebetween may not be consistent. Clamping adds to the time and cost required to make such a construction member.
Furthermore, certain applications require the joists to withstand forces that are applied in different directions or forces that are not applied uniformly along the length of the joist. One example of such problems is found in the engineered joists used to support a manufactured or xe2x80x9cmobilexe2x80x9d home. Such homes are generally constructed in one or two large sections and then transported by tractor trailer to a home site at which point they are placed on a fixed foundation. The modular homes are generally rectangular so that they will fit on a trailer. The joists that support the structure generally run the width of the home, which direction corresponds to the width direction of the trailer. However, joists are normally designed to be supported near their ends, such as when the home is placed on a foundation. On the trailer, however, the support comes at locations closer to the middle of the width of the structure. Supported in this manner, the joists and the manufactured homes are subject to flexure during the moving process, and this can lead to cracked interior walls and other problems when the home is transported. One method to address this problem would be to use over-manufactured joists that could withstand such stressesxe2x80x94however, as these stresses occur only for several hours of the many-year life span of a home, this method unnecessarily increases costs. It would therefore be desirable to provide an engineered joist that can be assembled without clamping, that provides additional support only in certain locations, and that resists the twisting and other unusual forces experienced by joists used in a manufactured home when the home is being transported.
These and other problems are addressed by the present invention which comprises an engineered construction member or joist comprising, in a first embodiment, top and bottom chords connected by a web, which web has non-linear, profiled end portions that are received in correspondingly shaped profiled grooves in the chords. Because these profiled end portions provide a mechanical connection between the chords and web, the need to clamp the upper and lower chords together when the web is glued to the chords is reduced or eliminated. It has also been found that these profiled end portions seem to provide greater strength and rigidity to the joists, especially when forces are applied in different directions when the joist and structure in which it is incorporated, is moved. While a primary use for such joists is envisioned to be in the manufactured home market, other applications where joist are subject to a forces in a variety of different directions can readily be imagined.
In a second embodiment of the invention, a joist is provided with a two-piece web member that can be inserted at any needed location along the joist to provide additional support between the chords at the locations where a large load is to be supported. Advantageously, these web members can either be installed when the joist is manufactured or alternately, in the field when a structure incorporating the joist is being attached to another structure. For example, the web element can be placed where needed to provide additional support during the transport of a manufactured home, removed at the job site, and replaced with a second element at a different location along its length, such as under a load supporting wall, where needed. Since the web element is easy to install and remove, the element used during transport can be removed at the job site so as not to interfere with the placement of wiring and plumbing, etc. in the finished structure. And, when the vertical supports that surround the center chase of a joist are replaced with web members, it becomes possible to provide wider chases than has heretofore been feasible without unduly weakening the construction member.
It is therefore a primary object of the present invention to provide an improved constructional member with increased rigidity.
It is another object of the invention to provide an improved constructional member having chords connected by webs which are attached to the chords at profiled end portions.
It is yet another object of the invention to provide a construction member than can be assembled without clamping.
It is a further object of the invention to provide selectively insertable support webs for an engineered joist.
It is still another object of the invention to provide a method of selectively reinforcing a joist at a given location along its length.
It is still a further object of the invention to provide an engineered joist having a larger than normal central or other chases.
It is yet another object of the invention to provide an engineered joist with trimmable ends which include web portions with profiled end portions routed into upper and lower chords.